There are three ways for you to implement the Word Add-In for you and your organization. 


If your organization allows individual users to install Add-Ins, then installing via the Microsoft AppSource is your best route.


Install via Microsoft AppSource

https://docs.microsoft.com/en-us/office/dev/store/submit-to-appsource-via-partner-center


For an individual, wanting to learn how to install themselves, see also: How do I download the Word Add-On?


If your organization requires tighter authorization, your IT department can use one of the following options.


Install via Microsoft 365 Admin Center

https://docs.microsoft.com/en-us/microsoft-365/admin/manage/test-and-deploy-microsoft-365-apps?view=o365-worldwide


Install via Sharepoint Catalog

https://docs.microsoft.com/en-us/office/dev/add-ins/publish/publish-task-pane-and-content-add-ins-to-an-add-in-catalog